1. Field of Invention
The present invention relates to a method of detecting an arc and an apparatus for controlling high-frequency arc discharge, which can control arc discharge without stopping the glow discharge in a high-frequency sputtering apparatus or a high-frequency etching apparatus.
2. Description of the Related Art
In the sputtering apparatus, for example, glow discharge is achieved in a predetermined space. Electric power is supplied to the apparatus from a high-frequency power source in order to perform sputtering on, particularly, insulation. During the high-frequency sputtering the glow discharge may abruptly change to arc discharge, inevitably damaging the sample. Generally, the greater the electric power, the more likely arc discharge will occur. That is, as the power is increased to raise the sputtering speed, an arc does not disappear quickly once it has been generated even in a region where arcs are less likely to develop. As the power is further increased, the arc remains in that region and would not disappear.
Apparatuses for controlling arc discharge are known, which are designed to interrupt the supply of power for 200 μs when the glow discharge is detected to have changed to arc discharge.
When this type of an apparatus interrupts the supply of power for 200 μs, however, not only the arc discharge but also the glow discharge is stopped. This is a problem.
An arc-discharge control apparatus is known, which interrupts the supply of power for 5 μs only when the glow discharge is detected to have changed to arc discharge. This apparatus is shown in FIG. 5 and disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-133412.
This apparatus will be described with reference to FIG. 5. As FIG. 5 depicts, a high-frequency power source PS is provided, which outputs a high-frequency voltage of 13.56 MHz. The high-frequency power source PS is connected to a target T and a chamber CH by a coaxial cable, a power meter CM, a coaxial cable, an impedance-matching circuit IM and a DC-cutting Cc. Thus, power is supplied from the high-frequency power source PS, applying a voltage between the target T and the chamber CH. “GD” in FIG. 5 is a glow-discharge device.
Reflected-wave voltage Vr and traveling-wave voltage Vf are input to amplifiers 1 and 2, respectively, instead of the traveling-wave voltage and reflected-wave voltage that are acquired from the power meter CM. Further, they are input to a comparator 5 via differentiating circuits 3 and 4, respectively. When the value dVr/dt−dVf/dt reaches the first level set by a level-setting unit 6, which is, for example, 0.2 or more, the comparator 5 outputs an H-level signal to a mono-multi circuit M/M. Upon receipt of the H-level signal, the mono-multi circuit M/M outputs an arc-cutting pulse to the high-frequency power source PS. Note that the arc-cutting pulse has a predetermined length T1, which is, for example, 5 μs.
To be more precise, the mono-multi circuit M/M supplies an arc-cutting pulse to the high-frequency power source PS as shown in FIG. 4B, when the reflected-wave voltage Vr rises to a peak as shown at a in FIG. 4A. The high-frequency power source PS inevitably stops applying a voltage between the target T and the chamber CH. Consequently, the arc discharge cannot be detected even if the reflected-wave voltage Vr changes as shown at b in FIG. 4B. This is because the value dVr/dt−dVf/dt does not exceed the first level. Nor can the arc discharge be detected while the voltage Vr remains at a certain level because the arc keeps existing. That is, the output of the comparator 5 is the value of 0 as long as both the reflected-wave voltage Vr and the traveling-wave voltage Vf stay at certain levels. In this case, the dVr/dt−dVf/dt fail to rise above the first level, making it impossible to detect the arc discharge.